1. Field of the Invention
The present invention relates to vehicle live hub wheel end systems in general, and, more particularly, to a central tire inflation system for steering live hub wheel ends.
2. Description of the Prior Art
Central tire inflation systems (CTIS) are becoming popular with the trucking industry, especially for off-road vehicles. Various types of tire inflation system have been developed both for trailer axles and tractor drive axles.
The central tire inflation system allows the operator to control the air pressure of the tires for improved performance of the tires and of the vehicle. However, the central tire inflation systems currently available suffer from two primary drawbacks. The axle and hub and possibly other parts must be extensively modified in order to accommodate a conventional system.
The off-road vehicles often drive on soft, muddy surfaces and then switch to harder surfaces, such as paved roads. To obtain proper traction on soft, muddy surfaces, the tire should be operated at a relatively low pressure. To obtain proper traction and optimal fuel mileage on harder surfaces, the tires should be operated at relatively high pressures. The differences between preferred high tire pressures (hard surfaces) and preferred low tire pressures (soft surfaces) may be quite large. For example, some truck tire manufacturers recommend a maximum tire pressure of 120 psi for highway conditions and 8 to 15 psi for extremely soft conditions such as sand, mud and swamps. A tire pressure for intermediate road conditions may be approximately 40 psi. Of course, in the case of trailers, the preferred tire pressure will also be dependent upon the weight of the goods or equipment carried in the trailer.
The central tire inflation system is adapted to provide compressed air from a remote pressurized air source to a pneumatic tire of a motor vehicle. Since the tire is rotating and the pressurized air source is stationary, the typical tire inflation system includes some kind of sealing means located between a stationary hub member of the wheel end assembly and a rotating tire-mounting hub. The typical tire inflation system also is provided with a conduit that extends from the sealing means through the wheel end assembly to the pneumatic tire. It has been found particularly difficult to design the tire inflation system for live hub wheel ends, especially for the live hub wheel ends of front drive/steering axles wherein pressurized air is transmitted from the fixed inflation air source to pneumatic tires mounted on steering wheels of the drive axle.
Current systems are quite complex, cumbersome and expensive, and require a great deal of changes in the current production wheel end design.
The present invention alleviates the drawbacks of the prior art. The present invention provides a central tire inflation system for a steering live hub wheel end assembly providing a unique arrangement for a steering driving axle of a motor vehicle that minimizes changes in the current production wheel end designs.
In the preferred embodiment disclosed, the live wheel end assembly comprises a steering knuckle secured to the vehicle, and a spindle assembly rotatably mounted about the steering knuckle. An inlet passageway is formed directly through the steering knuckle. The bearing assembly receives the coaxial spindle assembly to which a pneumatic tire is mounted. A drive shaft is rotatably disposed through the steering knuckle and is in driving connection with the spindle assembly.
The spindle assembly has a central axial bore provided with a spline section. The drive shaft has a spline portion and a flange portion. The drive shaft is inserted through the central spindle bore such that respective splined portions form a spline connection.
A rubbing slip-ring seal assembly is mounted into a flange of the steering knuckle. The slip-ring seal assembly includes a pair of axially spaced rotary seal members and defines a seal chamber therebetween. The first seal member is in sliding sealing contact with an outer peripheral surface of a sealing lip portion of the spindle assembly, while the second seal member is in sliding sealing contact with an outer peripheral surface of the flange portion of the drive shaft.
The inlet passageway transmits pressurized air from a pressurized air source directly to the sealed chamber. An outlet passageway is formed directly through the spindle assembly and is also in direct communication with the seal chamber to establish communication between the seal chamber and a pneumatic tire.
In accordance with the first exemplary arrangement of the present invention, the spindle assembly includes a wheel hub member and a coupling ring member adapted to drivingly couple the drive shaft to the wheel hub member. In this embodiment, the outlet passageway is formed directly through the coupling ring member, and the first seal member is in sliding sealing contact with an outer peripheral surface of a sealing lip portion thereof.
In accordance with the second exemplary arrangement of the present invention, the spindle assembly includes a wheel hub member directly drivingly coupled to the drive shaft. In this embodiment, the outlet passageway is formed directly through the wheel hub member, and the first seal member is in sliding sealing contact with an outer peripheral surface of a sealing lip portion thereof.
Therefore, the arrangement of the central tire inflation system for the steering live hub wheel end assembly in accordance with the present invention provides a shortened reliable flow path between the steering knuckle and the spindle assembly in the live spindle wheel end assembly. The present design also requires less seals than the related art and provides a simpler arrangement reducing manufacturing costs and assembly time to provide an overall superior seal interface arrangement reducing potential leakage and increasing reliability. Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings.
These and other benefits of the present invention will become apparent from the following description and associated drawings.